Photochromic multifocal lenses and method of fabrication thereof

ABSTRACT

A high index of refraction, low softening point, low expansion segment glass is fused into a countersunk photochromic glass blank of lower index of refraction. The high index of refraction segment is primarily composed of SiO2, B2O3, and PbO with lesser amounts of other oxides.

United States Patent Upton *Oct. 28, 1975 PHOTOCHROMIC MULTIFOCAL LENSES [56] References Cited AND METHOD OF FABRICATION UNITED STATES A T THEREOF 3,480,453 11/1969 Reid et al 106/47 R Inventor; Lee 0, Upton, Sturbridge Mass 3,529,980 9/1970 Brower 106/47 Q 3,535,133 10/1970 Akhtan 106/53 [73] Assrgnee: American Optical Corporation, 3,653,933 4/1972 Tsuvekawa 106/47 Q Southbridge, Mass. 3,801,336 4/1'974 Upton 106/53 Notice: The portion of the term of this patent subsequent to p 2, 1991 Pm71ary Examiner-L. Dewayne Rutledge has been disclaime 7 Assistant Examzner-Mark Bell Attorney, Agent, or Firm-H. R. Berkenstock ln; [22] Filed: Nov. 9, 1973 William C. Nealon 21 Appl. No.2 414,476

R l t d U S A r [57] ABSTRACT e i pp canon Data A high index of refraction, low softening point, low [63] f g g g 3 expansion segment glass is fused into a countersunk 9 3301 photochromic glass blank of lower index of refraction. 52 us. c1. 106/53; 106/47 Q; 106/54 32 1:? 1a: gigjfjjf; ggfiigflgfifigijfi;"g; [51] Int. Cl. C03C 3/08; C03C 3/10; C03C 3/30 other oxides [58] Field of Search 106/53, 54, 47 Q 8 Claims, 6 Drawing Figures US. Patent Oct. 28, 1975 PHOTOCI-IROMIC MULTIFOCAL LENSES AND METHOD OF FABRICATION THEREOF This is a continuation-in-part of application Ser. No. 333,835 filed Feb. 20, 1973, now US. Pat. No. 3,801,336.

BACKGROUND OF THE INVENTION 1. Field of the Invention Fused glass multifocal lenses with particular reference to multifocal lenses having major portions formed of photochromic glass and glass segment portions of lower refractive index fused thereto.

2. Description of the Prior Art Multifocal lenses having segment portions of high refractive index glass fused to major portions of relatively low refractive index glass are common in the art as evidenced by US. Pat. Nos. 2,755,706 and 2,958,162. Glasses used for the segment and major portions of such lenses, i.e. having compatible coefficients of expansion and softening temperatures, are readily available in colors or clear.

Since, however, these segment glasses do not provide a compatible expansion fit and do not have softening temperatures low enough to prevent impairment of the photo-response of known photochromic glass major portions after fusion, the manufacture of photosensitive multifocal lenses has been restricted either to those of one-piece construction of the type shown in US. Pat. Nos. 2,410,145 and 2,890,551, for example, or of the cemented type wherein the segments are cemented into countersinks of of major portions of the lenses or the alternative of a photochromic overlay.

Cemented glass multifocal lenses are currently becoming obsolete in view of their not being able to withstand air-toughening temperatures or ion-exchange processing now used and/or contemplated for future use in the finishing of lenses for customer wearing purposes.

In the light of occupational safety and health regulations now requiring all glass lenses to be toughened either by air hardening or ion exchange process before wearing, glass photosensitive multifocal lenses capable of withstanding the required toughening processes have, heretofore, become extremely difficult if not impossible to produce. The cemented type tends to delaminate and/or otherwise become interfacially defective, while, on the other hand, impairment of the required or desired photoresponse characteristics of photochromic lens major portions and interfacial defects result from attempts to fuse segment portions of conventional high refractive index glasses to the photochromic major portions.

, the high index segment glass having a softening temperature which is low enough to prevent impairment of photoresponse of the photochromic major portion glass during the operation of thermally sealing (i.e. fusing) the segment glass to the photochromic major portion glass.

Another object of the invention is to provide a family of high refractive index glasses suitable for thermal scaling to currently available low refractive index photochromic glasses without impairment of the photoresponse of the latter glasses and to provide improved multifocal lenses incorporating these high and low re-. fractive index glasses,

The invention will be more readily understood from the following detailed description taken in conjunction with the accompanying drawings.

IN THE DRAWINGS FIG. 1 is a front elevational view of a fused multifocal lens of a type which is pertinent to this invention;

FIG. 2 is a view in cross-section, of a segment component useful in the manufacture of lenses of the type illustrated in FIG. 1;

FIG. 3 is a cross-sectional view of an assembly of major and segment portions of glass from which a multifocal lens of the type illustrated in FIG. 1 may be formed;

FIG. 4 is a front elevational view of another type of fused multifocal lens:

FIG. 5 is a frontal view of a segment component useful in the manufacture of lenses of the type illustrated in FIG. 4; and

FIG. 6 is a view, in cross-section, of an assembly of major and segment portions of glass from which a milltifocal lens of the type illustrated in FIG. 4 may be formed.

DESCRIPTION or THE PREFERRED EMBODIMENTS Examples of photochromic glasses known and used for ophthalmic lenses are given in US. Pat. Nos. 3,208,860 and 3,449,103. r

The disclosure of the first-mentioned patent concerns inorganic silicate glasses containing submicroscopic crystals of a silver salt, e.g. silver chloride, silver bromide, silver iodide, all of which become darker in color when the glass is subjected to actinic radiation. The glasses regain their original color when the radiation is removed.

The latter US. Pat. No. 3,449,103 discloses still'another photochromic or phototropic glass useful for lenses or the like.

While various types of photochromic glass may be used for the present invention, a photochromic glass having the following analysis may be considered as typical of the type suitable for use in conjunction with improved segment glasses of the present invention:

TABLE I Oxide Weight Percent Glasses of the aforementioned type are manufactured by Corning Glass Works of Coming, N.Y., and sold under the trade names Photogray and Photosun. These are exemplary of photochromic glasses to which the present invention is especially applicable and they are currently identified by Corning Glass Works by order numbers 8097 and 8098 respectively.

These glasses may or may not be heat treated to produce or enhance their photochromic properties prior to their use in accordance with the invention. The fusion of segment glasses to heat treated (i.e. nucleated) photochromic type glasses (e.g. those having been subjected to heat treating temperatures of from 500 to 800C for periods of from as little as 1 minute to 16 or more hours) has been found to produce negligible, if any, adverse affect upon their photochromic properties. In the case of photochromic type glasses which have not been heat treated (i.e. unnucleated glasses) the heat used for segment fusion according to this invention has been found to develop and/or enhance their photochromic properties and obviate the need for separate heat treatment.

In producing fusion with little or no distorted interface between a low refractive index major portion and a high refractive index segment, the low refractive index glass should have a higher viscosity at the fusion temperature than the segment. Preferably, the low refractive index photochromic major portion would have a refractive index of from 1.50 to 1.55 and the refractive index of the segment glass would be within the range of from 1.59 to 1.70. At fusing temperature, the viscosity of the high refractive segment glass should be lower by about three orders of magnitude than the viscosity of the low refractive index major portion glass. It has been found that, under these conditions, fusion stress of the fused glasses is usually less than 30 kg/cm.

The high refractive index segment glass is formed generally of silicon dioxide, boron oxide and lead oxide, with minor amounts of other oxides. Ranges of ingredients useful for forming this high refractive index segment glass, according to the invention, are given in the following table:

TABLE 11 Weight Percent SiO, 16 36 13,0, 14 33 A1 8.5 10.5 ZnO 4.2 5.4 BaO 1.9 2.5 A 0; 0.25 0.35 PbO 27 36 sb,o, 1.4 2.0 X 0 0 2 Na,O 0 l T10, 0 5 L1 0, 0 6

Generally the high index segment glass has a composition within the ranges set forth in table IIA as follows:

TABLE II A Weight Percent n BaO 1.9 2.5 As,0, 0.25 0.35 Pbo 27 36 Sb,0, 1.59 1 9 K,O 0 2 Na o 0 l T10, 0 4 La o, 0 6

The preferred high refractive index segment glasses are those with a composition as defined in table 113 as follows:

TABLE II B Weight Percent SiO, 20 32 B 0 17 30 A1 0 9 l0 ZrlO 4.6 5.0 B30 2.1 2.3 AS203 0.25 0.35 PbO 30 33 sb o, 1.5 1.9 T10 2 3.5 La O 2 6 The high refractive index segment glass is prepared by mixing its ingredients for about five minutes, heating the mixture to melting temperature, fining the resulting glass of the melt and then casting the fined glass into the form of a flat sheet or a multiplicity of lens segments. After annealing and cooling, the cast segments or segments cut from a cast sheet of the resulting glass may then be ground and polished to the size and shape desired.

A preferred composition for the high refractive index segment glass is as follows:

EXAMPLE I Weight Percent S10, 20.50 B 0, 21.90 A1 0 9.60 ZnO 4.80 BaO 2.20 AS303 0.30 PhD 3 I .50 S15 0: 1.7

A batch of glass formed of the foregoing composition in the proportions of ingredients given in the following Example IA will have an index of refraction of approximately N =l .6706, N =1.6584, N =l .6537, where 486, 589 and 656 are wavelengths of light in millimicrons. Its strain point will be approximately 893F, anneal point approximately 944, and fiber softening point 1 151F.

The glass of this composition (Example IA) was formed by mixing all of its ingredients together and melting the mixture in a platinum crucible. The crucible was placed in a furnace wherein its temperature was raised over a period of about 4 hours from room temperature to a temperature between 2600 and 2650F to melt the ingredients. The melt was maintained, for the purpose of fining, at a temperature of about 2600F for a period of about 16 hours. A temperature within shown in FIG. 4. This lens (FIG. 4) is of the type having a segment 14 with a flat or straight upper edge 22. Such a multifocal lens 10' is commonly referred to in the art as a cutoff style fused multifocal. Its upper the range of from 2300 to 2650F, held for a period of 5 edge 22 may be arcuate with a slightly upwardly difrom 1 to 16 hours, will produce similar results. rected curvature which blends smoothly into the curva- Following the fining cycle, the furnace temperature ture of the lower portion of the segment or acutely joins was gradually lowered to approximately 2000F and the depending curvature of the segment. the melt was stirred for approximately 4. hours at In the manufacture of the cutoff fused multifocal, its 2000F. 10 segment 14' (FIG. 5) is formed of two pieces 24 and 26 After stirring, the glass was cast at approximately the each cut, ground and polished to the general configurasame 2000F temperature onto an iron plate, annealed tion shown in FIGS. 5 and 6. Piece 24 has the aforeand cooled and then cut, ground and polished into a mentioned straight upper edge 22. Piece 26 is formed multiplicity of pieces each of the configuration desired 01'' a photochromic glass, preferably identical to the for use as a segment or as a portion of a segment adaptglass used for major piece 12' and is edge fused, e.g. at able to fusion to a photochromic major piece of glass 8 mperature of ppr ximately 5 to piece 24 o for the making of a fused multifocal lens. segment '14. The two pieces 24 and 26 are then pro- Referring more particularly to the drawings, there is vided with a ground and polished face 16' and, as a illustrated in FIG. 1 as fused multifocal lens 10 having unit. fused into countersink major piece a major portion 12 formed of a photochrornic glass, e.g. Multifocal ens 10' is formed by grinding and polishof the composition set forth hereinabove under Table ing the fused assembly of segment 14' and major piece I and a segment 14 of a relatively high refractive index 12' to a finished shape and size, e.g. along lines 20' and glass, e.g. of the composition set forth in Example IA. 21'. Those interested in greater'details of the forming In the making of multifocal lens 10, segment 14 (FIG. of cutoff style fused multifocal lenses may refer to US. 2), after having been cast or cut from the aforemen- Pat. No. 1,899,777, for example. In the manufacture of tioned high refractive index glass, is customarily the two piece fused segment 14' of FIG. 5 a preferred ground and optically polished on a side 16 to a sphericomposition for the glass of portion 24 is that listed cal curvature corresponding to the curvature of a coununder column 9 of Table III which follows.

TABLE III Oxide 2 3 4 s 6 7 8 i 9 S10 20.00 24.00 28.00 32.00 26.00 24.00 21.00 20.00 13,0 29.90 25.90 21.90 17.90 21.90 21.90 21.90 21.90 A120; 9.60 9.60 9.60 9.60 9.60 9.60 9.60 9.60 ZnO 4.80 4.80 4.80 4.80 4.80 4.80 4.80 4.80 B 2.20 2.20 2. 20 2.20 2.20 2.20 2.20 2.20 145,0 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 PbO 31.50 31.50 31.50 31.50 31.50 31.50 31.50 31.50 5020, 1.70 1.70 1.70 1.70. 1.70 1.70 1.70 1.70 T102 2.00 2.00 3.00 3.00 1.2 03 2.00 4.00 5.00 N, 1.6153 1.6172 1.6136 1.6109 1.6311 1.6430 1.6572 1.6642 S.T.F 1099 1138 1161 1198 1149 1160 1158 1166 a x 10 52 51 47 49 54 51 55 a coeflicient of expansion tersink 18 which is also ground and polished into the 45 TABLE A major piece 12 of lens 10. Surface 16 of segment 14 may be formed to a curvature of slightly shorter radius Oxide 10 11 12 13 14 than that of countersink 18 for purposes of initially making point contact with countersink 1s and thereby ii, $13 5}, ii, 2 3 expressmg air and gases radially outwardly of counter- 6 3 -0 10.1 9.6 9.6 9.6 sink 18 as segment 14 is caused to gradually asume the :28 2:3 2:: 2:3 2:; 3:; countersink shape when heated for fusion thereto, e.g. A620, .35 .25 .3 .3 .3 at a temperature of approximately 1150F and held at 52 i? the fusing temperature for a period of time of approxino, 055 2:0 5 2:75 mately from 7 to 10 minutes. Following the fusion of E l segment 14 to countersink 18 of major piece 12, grindi I 1 I I I ing and polishing of the resultant assembly shown in FIG. 3 along lines 20 and 21, for example, will complete opposite sides of the fused multifocal lens 10. The above glasses have an index of refraction, Strain Those interested in greater details of this technique for POint and coefiident of p i n Substanforming a fused multifocal lens may refer to US. Pat. tially corresponding to those of EXAMPLE I and ex- No. 2,958,162. arnples 2-9 of Table III. These glasses are suitable for While FIGS. 1-3 illustrate the making of a multifocal forming multifocal lens segments according to the preslens having a segment 14 of circular configuration, it cut invention.

should be understood that the present invention is equally applicable to the making of multifocal lenses having segments of different shapes, e.g. of the type Following the procedure outlined above relative to Example I, a series of high refractive index glasses may be manufactured which have compatible expansion co- 810 I6 36 B 14 33 A1 0 8 5 10.5 ZnO 4.2 5.4 BaO 1.9 2.5 A5 0; 0.25 0.55 PbO 27 36 Sb O 1.4 2.0 2 0 2 Na o 0 l TiO 0 5 La O 0 6 2. A glass according to claim 1 consisting essentially of the following ingredients in the range of weight percent:

SiO, 20 32 B 0, 17 30 9'19 4 3 l". n BaO 1.9 2.5 A5 0 0.25 0.35 PbO 27 36 Sb O, 1.59 1.9 K 0 0 2 Na o 0 1 H0, 0 4 1.21 0. 0 6

3. A glass according to claim 1 consisting essentially of the following ingredients in the range of weight percent:

SiO, 20 30 B 0; 17 30 as .211. n 330 2.1 2.3 A5 0; 0.25 0.35 PbO 30 33 Sb O l.5 1.9 TiO: 2 3.5 L3 0: 2 5.5

4. A glass according to claim 1 consisting essentially of the following ingredients by weight percent:

SiO, 32 B 0 16.4 A1 0: 9.0 ZnO 5.2 8210 2.0 A o, .35 PbO 33.0 Sb,0 1.5 Ti0 0.55

5. A glass according to claim 1 consisting essentially of the following ingredients by weight percent:

510 28.45 3,0 21.9 A1 0 10.1 ZnO 4.2 BaO 2.5 A5 0 .25 PhD 27.1 515 0;, 1.9 K 0 1.1 Na O .5 F10 2.0

6. A glass according to claim 1 consisting essentially of the following ingredients by weight percent:

SiO; [8 B 0; 31.9 Al O 9.60 ZnO 4.80 BaO 2.2 A5 0; 0.3 H30 31.50 Sb O; 1.7

7. A glass according to claim 1 consisting essentially of the following ingredients by weight percent:

SiO 23 B 0; 21 .9 Algog 9 .6 ZnO 4.8 H20 2.2 A5 0; .3 PhD 3 l .5 Sb O l .7 TiO, 5

8. A glass according to claim 1 consisting essentially of the following ingredients by weight percent:

SiOz 20.5 B 0 2 l .9 A1 0: 9.6 ZnO 4. 8 BaO 2.2 A5 0 .3 PhD 3 l .5 Sb O l .7 TiO, 2.75 La O 4.75 

1. A GLASS OF HIGH REFRACTIVE INDEX ADAPTABLE TO FUSIN WITH A PHOTOCHROMIC GLASS OF LOWER REFRATIVE INDEX CONSISTING ESSENTIALLY OF THE FOLLOWING INGREDIENTS IN THE RAGE OF WEIGHT PERCENT:
 2. A glass according to claim 1 consisting essentially of the following ingredients in the range of weight percent:
 3. A glass according to claim 1 consisting essentially of the following ingredients in the range of weight percent:
 4. A glass according to claim 1 consisting essentially of the following ingredients by weight percent:
 5. A glass according to claim 1 consisting essentially of the following ingredients by weight percent:
 6. A glass according to claim 1 consisting essentially of the following ingredients by weight percent:
 7. A glass according to claim 1 consisting essentially of the following ingredients by weight percent:
 8. A glass according to claim 1 consisting essentially of the following ingredients by weight percent: 